Contamination of glass surfaces by water, grease, dirt, dust, or any other substance, can be a problem in a range of circumstances. In applications such as windows or vehicle windscreens, it is important to maintain excellent optical clarity through the glass panel. In the example of the vehicle windscreen, contamination such as rain or dirt on a windscreen panel can obscure the driver's view and create a driving hazard. There is a need to detect the presence of contamination and provide a response mechanism, such as activating the use of windscreen washer fluid and windscreen wipers. US20070096015 A1 describes the use of FTIR (frustrated total internal reflection) to determine the presence of rain on the surface of a vehicle windscreen by directing a beam of light into the glass windscreen. When the windscreen is clean, the beam of light is totally internally reflected and received by a sensor. When the windscreen is wet, the light is absorbed by the water and the total internal reflection is frustrated. The change in the reflective properties of the glass can be detected in order to determine the presence of rain on the glass.
Other examples of glass (or simply transparent) panels that might benefit from a means for detecting the presence of contamination may include shop windows or museum displays, where the need for optical clarity is high, while the risk of contamination from human hands is also high. Human fingers usually deposit grease on the surface of any object they touch and, over time, the build-up of grease can result in a visible dirty effect on the touched surface.
In certain applications, the presence of surface contamination on a transparent panel may have consequences that extend beyond merely degrading the optical clarity of the panel. Touch sensitive panels, such as those used on touch sensitive displays, are known to suffer from performance degradation when the touch sensitive surface is contaminated with water, finger grease, etc. This effect can be observed particularly with projected capacitive touch technology and in-glass optical touch technologies using techniques such as scatter detection or detection of light attenuation. An example of an FTIR optical touch technology which might suffer from contamination is shown in U.S. Pat. No. 7,432,893. Further examples of touch sensitive systems operating by FTIR are disclosed in U.S. Pat. No. 8,581,884, US 2013/0044073 and US 2011/0074735. Therefore, there may be a particular need for a touch sensitive surface to detect and react to surface contamination of a touch sensitive panel.
In other applications, the presence of surface contamination may represent additional problems beyond those of optical performance or touch performance. In the field of medical instruments, it may be critical that certain surfaces remain free of contamination which may host infectious agents. The use of a touch display in an operating theatre, for example, may allow surgeons to access vital information during a surgical operation. However, if the touch display becomes contaminated with fluids or dirt during the operation, it might be critical that the display is able to detect and react to the contamination.
Therefore, there is a need for an accurate and fast method of determining contamination of a transparent panel which can provide contamination information across a contamination sensitive area.